1. Field of the Invention
The present invention relates to a laser beam projection apparatus used for a setting or survey operation in construction or the like and, more particularly, to a laser beam projection apparatus having an automatic grade correction unit for automatically correcting the direction of a laser beam when the projection apparatus main body is tilted.
2. Related Background Art
As a conventional laser beam projection apparatus having an automatic grade correction unit, an apparatus shown in FIGS. 16 and 17 is known (Japanese Patent Application Laid-open No. 63-222214).
FIG. 16 is a longitudinal sectional view of a conventional laser beam projection survey apparatus having an automatic grade correction unit. FIG. 17 is a longitudinal sectional view showing a state wherein the laser beam projection survey apparatus in FIG. 16 is tilted.
A leveling unit 1108 is arranged under a laser beam projection apparatus main body 1109. A laser diode 1101 is arranged at an upper portion in the projection apparatus main body 1109 to emit a laser beam La in the lower direction. An automatic grade correction unit is arranged under the laser diode 1101.
The automatic grade correction unit has a projection lens 1102 for collimating the laser beam La emitted from the laser diode 1101 in the lower direction into a parallel beam, and a transparent vessel 1103 through which the parallel beam from the projection lens 1102 is transmitted. The interior of the transparent vessel 1103 is partitioned into two, upper and lower chambers. Silicone oils 2000 and 2001 are sealed in the chambers, and spaces 1108a and 1108b are formed at the upper portions of the respective chambers in contact with the liquid surfaces of the silicone oils 2000 and 2001. An upper flat portion 1103a, a central flat portion 1103b, and a lower flat portion 1103c of the transparent vessel 1103 are parallel to each other.
As shown in FIG. 17, when the projection apparatus main body 1109 is tilted at an angle .theta., the silicone oils 2000 and 2001 in the transparent vessel 1103 form sphenoidal shapes having gradient pitches .theta.. The laser beam La which is emitted from the laser diode 1101 and collimated by the projection lens 1102 is refracted when the laser beam La is transmitted through the sphenoidal (or wedge-shaped) silicone oils 2000 and 2001, and is output from the projection apparatus main body 1109 as a laser beam La having a deflection angle .theta.'.
When the refractive indices of the silicone oils 2000 and 2001 are respectively represented by n2000 and n2001, a correction condition formula .theta.=(n2000 +n2001-2).theta. is given. When silicone oils 2000 and 2001 with n2000=n2001=1.5 are used, grade correction of the laser beam La is realized. More specifically, the laser beam La is automatically corrected to direct in the vertical direction, so that any measurement error caused by tilt of the projection apparatus main body 1109 is corrected.
However, there is no silicone oil having an appropriate viscosity and a proper refractive index of 1.500, and in fact, silicone oil having a refractive index of 1.49 or 1.51 must be used. Therefore, if the above correction condition formula is used, the correction accuracy is degraded. On the other hand, when the automatic grade correction unit is used within a range not to degrade the correction accuracy, the correction range of the automatic grade correction unit becomes as narrow as, e.g., about .+-.10 minutes. As a result, a leveling operation for rotating the leveling screw 1108 while observing the bubble tube must be performed, resulting in troublesome setting of the laser beam projection apparatus.
In addition, the conventional laser beam projection apparatus projects a laser beam to form a vertical plane. For this reason, to perform a setting operation by vertical plane laser beam projection and a setting operation by horizontal plane laser beam projection, laser beam projection apparatuses dedicated to the respective operations must be prepared.
Furthermore, the laser beam La after grade correction is output only in the lower direction. Therefore, this apparatus cannot be used for an ink projection operation (an operation for transferring ink, i.e., a point on the floor to the ceiling) performed in an interior finish work or the like of a building.